Conventionally, for a fine metal terminal for establishing an electrical connection with an external part on the front face of a semiconductor substrate, a gold (Au) bump or the like is used. This Au bump is formed by plating and thus has a large surface roughness. To planarize such a metal terminal, a chemical mechanical polishing (CMP) method is used. This method presses a flat polishing pad against a metal and a resin, which are faces to be processed have been formed relatively flat in advance, to planarize with high accuracy their surfaces chemically and mechanically using slurry (a chemical polishing agent). The CMP is finished at a stopper layer which is a rigid resin or a metal face provided in advance. The CMP method is a method not depending on a TTV (total thickness variation) that is defined by variations in thickness of a semiconductor substrate or by the difference between a maximum thickness and a minimum thickness of a semiconductor substrate.
Further, to join the Au bump or the like in the conventional art that has a large surface roughness, a mounting method is required that loads the bump with a load, heat, ultrasound, or the like until the roughness is eliminated.
In addition to the CMP, some other planarizing methods using, for example, a cutting tool have been devised (see, for example, Japanese Patent Application Laid-open No. Hei 7-326614, Japanese Patent Application Laid-open No. Hei 8-11049, Japanese Patent Application Laid-open No. Hei 9-82616, and Japanese Patent Application Laid-open No. 2000-173954). However, any of them aims to planarize an SOG film within a partial region on an LSI, and is a method of cutting with reference to a face to be cut, which does not depend on the TTV of a semiconductor substrate similarly to the CMP. Further, there is another method of exposing a surface of a bump by cutting (see Japanese Patent Application Laid-open No. 2000-173954 (Japanese Patent Application No. Hei 10-345201)), which aims to planarize a bump portion formed on an LSI, and is a method of cutting with reference to a face to be cut, which does not depend on the TTV of a semiconductor substrate.
As described above, the Au bump is used for fine connection, but it is difficult to join the bumps because of the large surface roughness of the bumps. Further, when the CMP is used to concurrently planarize a metal such as Au and a resin, a depression called dishing appears caused by the difference in polishing speed between the metal and the resin. Due to the dishing, it is necessary to load the bump with a load, heat, ultrasound, or the like to reliably join the bumps.
The present invention has been developed in consideration of the above-described problems, and has an object to provide, in place of the CMP, a method for forming bumps, which makes it possible to planarize surfaces of fine bumps formed on a substrate at a low cost and a high speed and to connect the bumps with each other easily and reliably without causing any inconvenience such as dishing or the like, a reliable semiconductor device and a method for forming the same, and a semiconductor manufacturing apparatus.